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Creators/Authors contains: "Chamanzar, Maysamreza"

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  1. Abstract

    Ultrasonically-sculpted gradient-index optical waveguides enable non-invasive light confinement inside scattering media. The confinement level strongly depends on ultrasound parameters (e.g., amplitude, frequency), and medium optical properties (e.g., extinction coefficient). We develop a physically-accurate simulator, and use it to quantify these dependencies for a radially-symmetric virtual optical waveguide. Our analysis provides insights for optimizing virtual optical waveguides for given applications. We leverage these insights to configure virtual optical waveguides that improve light confinement fourfold compared to previous configurations at five mean free paths. We show that virtual optical waveguides enhance light throughput by 50% compared to an ideal external lens, in a medium with bladder-like optical properties at one transport mean free path. We corroborate these simulation findings with real experiments: we demonstrate, for the first time, that virtual optical waveguides recycle scattered light, and enhance light throughput by 15% compared to an external lens at five transport mean free paths.

     
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    Free, publicly-accessible full text available December 1, 2024
  2. Free, publicly-accessible full text available June 1, 2024
  3. We demonstrate novel trapezoidal and rectangular stratified trench optical waveguide designs that feature low-loss two-dimensional confinement of guided optical modes that can be realized in continuous polymer thin film layers formed in a trench mold. The design is based on geometrical bends in a thin film core to enable two-dimensional confinement of light in the transverse plane, without any variation in the core thickness. Incidentally, the waveguide design would completely obviate the need for etching the waveguide core, avoiding the scattering loss due to the etched sidewall roughness. This new design exhibits an intrinsic leakage loss due to coupling of light out of the trench, which can be minimized by choosing an appropriate waveguide geometry. Finite-difference eigenmode simulation demonstrates a low intrinsic leakage loss of less than 0.15 dB/cm. We discuss the principle of operation of these stratified trench waveguides and present the design and numerical simulations of a specific realization of this waveguide geometry. The design considerations and tradeoffs in propagation loss and confinement compared with traditional ridge waveguides are discussed.

     
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  4. A conventional optical lens can enhance lateral resolution in optical coherence tomography (OCT) by focusing the input light onto the sample. However, the typical Gaussian beam profile of such a lens will impose a tradeoff between the depth of focus (DOF) and the lateral resolution. The lateral resolution is often compromised to achieve amm-scale DOF. We have experimentally shown that using a cascade system of an ultrasonic virtual tunable optical waveguide (UVTOW) and a short focal-length lens can provide a large DOF without severely compromising the lateral resolution compared to an external lens with the same effective focal length. In addition, leveraging the reconfigurability of UVTOW, we show that the focal length of the cascade system can be tuned without the need for mechanical translation of the optical lens. We compare the performance of the cascade system with a conventional optical lens to demonstrate enhanced DOF without compromising the lateral resolution as well as reconfigurability of UVTOW for OCT imaging.

     
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  5. Abstract

    Targeted light delivery into biological tissue is needed in applications such as optogenetic stimulation of the brain and in vivo functional or structural imaging of tissue. These applications require very compact, soft, and flexible implants that minimize damage to the tissue. Here, we demonstrate a novel implantable photonic platform based on a high-density, flexible array of ultracompact (30 μm × 5 μm), low-loss (3.2 dB/cm atλ = 680 nm, 4.1 dB/cm atλ = 633 nm, 4.9 dB/cm atλ = 532 nm, 6.1 dB/cm atλ = 450 nm) optical waveguides composed of biocompatible polymers Parylene C and polydimethylsiloxane (PDMS). This photonic platform features unique embedded input/output micromirrors that redirect light from the waveguides perpendicularly to the surface of the array for localized, patterned illumination in tissue. This architecture enables the design of a fully flexible, compact integrated photonic system for applications such as in vivo chronic optogenetic stimulation of brain activity.

     
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  6. A conventional optical lens can be used to focus light into the target medium from outside, without disturbing the medium. The focused spot size is proportional to the focal distance in a conventional lens, resulting in a tradeoff between penetration depth in the target medium and spatial resolution. We have shown that virtual ultrasonically sculpted gradient-index (GRIN) optical waveguides can be formed in the target medium to steer light without disturbing the medium. Here, we demonstrate that such virtual waveguides can relay an externally focused Gaussian beam of light through the medium beyond the focal distance of a single external physical lens, to extend the penetration depth without compromising the spot size. Moreover, the spot size can be tuned by reconfiguring the virtual waveguide. We show that these virtual GRIN waveguides can be formed in transparent and turbid media, to enhance the confinement and contrast ratio of the focused beam of light at the target location. This method can be extended to realize complex optical systems of external physical lenses and in situ virtual waveguides, to extend the reach and flexibility of optical methods.

     
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